Low-frequency viscosity, density, and viscoelasticity sensor for downhole applications

ABSTRACT

Disclosed is an apparatus for estimating a property of a fluid downhole. The apparatus includes a carrier configured to be conveyed through a borehole penetrating the earth. A cantilever is disposed at the carrier and configured to move in the fluid upon receiving a stimulus. An actuator is disposed at the cantilever and configured to provide the stimulus at a frequency less than a lowest resonant frequency of the cantilever. A sensor is disposed at the cantilever and configured to sense a strain imposed on the cantilever due to movement of the cantilever in the fluid in order to estimate the property.

CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY CLAIM

This application claims the benefit of Provisional Application No. 61/491,409, entitled “LOW-FREQUENCY VISCOSITY, DENSITY, AND VISCOELASTICITY SENSOR FOR DOWNHOLE APPLICATIONS”, filed May 31, 2011, which is incorporated herein by reference in its entirety.

BACKGROUND

In geophysical industries such as for hydrocarbon exploration and production, geothermal energy, and carbon sequestration, it is important to characterize fluids deep in the earth. Boreholes are drilled into the earth in order to access these fluids. Borehole tools are then conveyed through the boreholes to perform measurements on downhole fluids. Typically, very high pressures and temperatures are encountered by the tools when they are disposed in a downhole environment.

Physical properties such as density, viscosity, and viscoelasticity of downhole fluids are important to know when performing measurements on particle and polymer laden fluid as in fracking fluid as well as in some drilling muds. It is also important to know the density and viscosity of reservoir fluids at the pressure and temperature of the reservoir in order to determine the permeability and flow characteristics of the reservoir. It would be well received in the drilling industry if a sensor would be developed to measure physical properties of downhole fluids at ambient conditions.

BRIEF SUMMARY

Disclosed is an apparatus for estimating a property of a fluid downhole. The apparatus includes a carrier configured to be conveyed through a borehole penetrating the earth. A cantilever is disposed at the carrier and configured to move in the fluid upon receiving a stimulus force. An actuator is disposed at the cantilever and configured to provide the stimulus force at a frequency less than a lowest resonant frequency of the cantilever. A sensor is disposed at the cantilever and configured to sense a strain imposed on the cantilever due to movement of the cantilever in the fluid in order to estimate the property.

Also disclosed is a method for estimating a property of a fluid downhole. The method includes conveying a carrier through a borehole penetrating the earth and moving a cantilever disposed at the carrier in the fluid with an actuator at a frequency less than a lowest resonant frequency of the cantilever. The method further includes sensing a strain imposed on the cantilever due to movement of the cantilever in the fluid using a sensor in order to estimate the property.

Further disclosed is a non-transitory computer-readable medium having computer-executable instructions for estimating a property of a fluid downhole by implementing a method that includes: moving a cantilever in the fluid with an actuator at a frequency less than a lowest resonant frequency of the cantilever, the cantilever being disposed at the carrier configured to be conveyed through a borehole penetrating the earth; and sensing a strain imposed on the cantilever due to movement of the cantilever in the fluid using a sensor in order to estimate the property.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:

FIG. 1 illustrates an exemplary embodiment of a downhole tool disposed in a borehole penetrating the earth;

FIG. 2 depicts aspects of an embodiment of a sensor configured to measure physical properties of a fluid;

FIG. 3 depicts aspects of another embodiment of a sensor configured to measure physical properties of a fluid;

FIG. 4 depicts aspects of a feedback control circuit for providing a constant strain to the sensor; and

FIG. 5 presents one example of a method for estimating a property of a downhole fluid.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosed apparatus and method presented herein by way of exemplification and not limitation with reference to the Figures.

FIG. 1 illustrates an exemplary embodiment of a logging tool 10 disposed in a borehole 2 penetrating the Earth 3. The Earth 3 includes an earth formation 4 that includes layers 4A-4C, each layer having a property distinguishable from the property of another layer. As used herein, the term “formation” includes any subsurface materials of interest that may be analyzed to estimate a property thereof. The logging tool 10 is supported and conveyed through the borehole 2 by a carrier 5. In an operation referred to as wireline logging, the carrier 5 is an armored wireline 6. In addition to supporting the logging tool 10, the wireline 6 can be used to communicate information between the logging tool 10 and equipment at the surface of the Earth 3. In another operation referred to as logging-while-drilling (LWD), the logging tool 10 is disposed at a drilling tubular such as a drill string or coiled tubing and is conveyed through the borehole 2 while the borehole 2 is being drilled. In LWD, the logging tool 10 performs a measurement of a property of a subsurface material generally during a temporary halt in drilling.

Still referring to FIG. 1, the logging tool 10 includes a formation fluid extraction device 11. The formation fluid extraction device 11 is configured to extract a sample of a fluid from the formation 4 through the wall of the borehole 2. The sample is then provided to an instrument 7, which is configured to perform a measurement of a physical property of the formation fluid. Non-limiting examples of the property include density, viscosity, and viscoelasticity.

Still referring to FIG. 1, the formation fluid extraction device 11 includes a probe 12 configured to extend from the device 11 and seal to the wall of the borehole 2. In order to keep the device 11 in place while sealing, the device 11 includes a brace 13 configured to extend from the device 11 and contact the wall of the borehole 2 opposite of the location where the sealing is being performed. After a seal is formed, pressure within the probe 12 is reduced to extract the fluid from the formation 4 and to cause it to flow into the device 11 from which it can be provided to the instrument 7.

Still referring to FIG. 1, the logging tool 10 includes a downhole electronics unit 8. The downhole electronics unit 8 can be configured to operate the logging tool 10 and/or communicate data 14 between the logging tool 10 and a computer processing unit 9 at the surface of the Earth 3. The data 14 can include measurement data and/or commands.

Reference may now be had to FIG. 2, which depicts aspects of the instrument 7. The instrument 7 includes a cantilever 20 configured to be moved in a fluid of interest by an actuator 21 disposed at the cantilever 20. The cantilever is configured to be at least partially disposed within the fluid and to move within the fluid when receiving a stimulus force from the actuator 21. Movement or deflection of the cantilever 20 can be related to a physical property of the fluid of interest. In one or more embodiments, the cantilever 20 extends from a base 22 that can be a substrate from which both the cantilever 20 and the base 22 are built. In one or more embodiments, the cantilever 20 moves or deflects about an edge of the base 22 from which the cantilever 20 extends.

The actuator 21 can be built integral to the cantilever 20 or the actuator 21 can be attached to the cantilever 20 such as by an adhesive. In one or more embodiments, the actuator 21 includes materials that can provide a moving force responsive to a stimulus applied to the materials. Non-limiting embodiments of materials for the actuator 21 include electrically conductive materials, magnetic materials, piezoelectric materials, joule heating materials, magnetostrictive and photostrictive materials. With a conductive material, an electric current flowing through the conductive material can interact with a magnetic field to cause the cantilever 20 to move. With a magnetic material, varying the intensity of an external magnetic field, such as by varying a magnetizing current through an electromagnet, can cause the cantilever 20 to move in relation to the magnitude of the magnetizing current. With a piezoelectric material, applying a voltage to that material can cause the cantilever 20 to move. With a magnetostrictive material, varying an intensity of a magnetic field in that material can cause the cantilever 20 to move. With a photostrictive material, applying light to that material can cause the cantilever 20 to move. It can be appreciated that the various materials used for the actuator 21 can be built integral to (i.e., within) the cantilever 20 or they can be deposited in one or more layers on the cantilever 20.

Still referring to FIG. 2, a sensor 24 is disposed at the cantilever 20 and configured to provide an output responsive to movement of the cantilever 20. In one or more embodiments, the sensor 24 is configured to measure a strain of the cantilever 20 caused by movement of the cantilever 20 in the fluid of interest. Hence, the measured strain of the cantilever 20 is indicative of an amount of movement, deformation, or flexing of the cantilever 20.

In one or more embodiments, the sensor 24 is a resistance strain gauge in which a resistance of the strain gauge is related to the strain experienced by the strain gauge. In one or more embodiments of the resistive strain gauge, as the cantilever 20 flexes, the resistance material of the strain gauge either compresses decreasing total resistance or stretches increasing the total resistance. Hence, a change of resistance of this strain gauge is related to a change in the measured strain and displacement or movement of the cantilever 20. In one or more embodiments, the sensor 24 is a magnetostrictive strain gauge, which uses a magnetostrictive material to sense strain. The magnetostrictive material has a magnetization that is related to the strain experienced by that material. Thus, in one or more embodiments, a coil can have a voltage induced in it by a changing magnetic field of the magnetostrictive material (related to the changing strain) as the cantilever 20 moves back and forth. As with the actuator 21, it can be appreciated that the sensor 24 can be built into the cantilever 20, such as with solid-state electronic fabrication techniques, or attached post-fabrication such as with an adhesive.

Still referring to FIG. 2, the cantilever 20 defines a first hole (or opening) 25 and a second hole (or opening) 26 and a center bridge element 29 between the two holes. In addition, the cantilever 20 in the embodiment of FIG. 2 defines a first side bridge element 27 and a second side bridge element 28. The bridge elements extend from the base 22 to a distal end of the cantilever 20. It can be appreciated that actuator(s) 21 and sensor(s) 24 can be at any of the bridge elements or combination of the bridge elements.

As noted above, movement or deflection of the cantilever 20 can be related to a physical property of the fluid of interest. Generally, measurement of the movement or deflection of the cantilever 20 as a function of time is made with respect to the stimulus force applied by the actuator 21. That is, displacement of the cantilever 20 over time is measured with respect to the stimulus applied by the actuator 21 in order to determine a damping factor of the cantilever 20 caused by the fluid of interest. Movement of the cantilever 20 can include the effects of bulk movement of the fluid and shearing of the fluid. The bulk movement is related to the density of the fluid and the shearing is related to the viscosity of the fluid. It can be appreciated that the sizes of the holes 25 and 26 can be selected or tuned to predominantly measure density or viscosity. Smaller holes result in a larger cross-sectional area of the cantilever 20 for predominantly measuring density. Larger holes result in a smaller cross-sectional area of the cantilever 20 for predominantly measuring viscosity. It can also be appreciated that the size of the holes 25 and 26 can be selected to provide a balance between measurements of density and viscosity. It can also be appreciated that holes 25 and 26 provide insulation between the various materials used for the actuator 21 on the various bridge elements.

Still referring to FIG. 2, an electronic device 23 is coupled to the actuator 21 and the sensor 24. The electronic device 23 is configured to apply an electrical, magnetic, or photonic stimulus to a material of the actuator 21. In order to perform displacement versus time measurements of movement or deflection of the cantilever 20, the actuator provides the stimulus at a frequency less than the lowest resonant frequency of the cantilever 20. This prevents resonance effects from affecting the measurement. In one or more embodiments, the measurement frequency is zero Hertz. It can be appreciated that low-frequency measurements provide for multiple measurements in a short time period resulting in measurements having increased precision and accuracy in addition to an increase in the signal-to-noise ratio of the measurements.

Reference may now be had to FIG. 3, which depicts aspects of another embodiment of the cantilever 20. In the embodiment of FIG. 3, a conductive element 31 extends or runs from the first side bridge element 27 to the second side bridge element 28 in a U-shape configuration. Current flowing in the conductive element 31 interacts with an external magnetic field created by a magnetic field source 30 to impart a force on the cantilever 20 causing the cantilever 20 to move in the fluid of interest. In one or more embodiments, the magnetic field source 30 is an electromagnet where the strength of the magnetic field is controlled by a magnetic field control signal, such as magnetizing current, from the electronic device 23. Hence, the electronic device 23 can control the amplitude and the frequency of movement of the cantilever 20 by controlling magnetizing current to the magnetic field source 30 that is an electromagnet. Further, in the embodiment of FIG. 3, each of the bridge elements 27, 28 and 29 includes one sensor 24. It can be appreciated that multiple sensors 24 provide for strain measurements having increased precision, accuracy, and signal-to-noise ratio.

Once measurements of the fluid of interest are performed using the cantilever 20, the resulting strain measurements of the cantilever 20 are used to estimate a physical property of the fluid of interest. Disclosed are at least two methods to estimate the physical property from the strain measurements. In one method, the instrument 7 is calibrated in a laboratory using samples of expected downhole fluids having known physical properties such as density, viscosity, and viscoelasticity. Hence, a measured response of the instrument 7 can be compared to the calibrated responses of the laboratory samples to estimate the physical properties. In another method, the strain measurements are input into mathematical relationships that use basic principles to relate the strain measurements to the physical properties.

One example of mathematical relationships relating a strain measurement to density is now presented where ε represents the strain measured by the sensor 24 where the sensor 24 is a resistive strain gauge.

$ɛ = \frac{\Delta \; {R/R_{G}}}{GF}$

where ΔR is the change in resistance caused by strain, R_(G) is the resistance of the undeformed sensor 24, and GF is the gauge factor.

$\tau = {\mu \frac{u}{y}}$

where τ is the shear stress exerted by the fluid (Pa), μ is the fluid viscosity—a constant of proportionality (Pa·s), and

$\frac{u}{y}$

is the velocity gradient perpendicular to the direction of shear, or equivalently the strain rate (s⁻¹).

The shear stress is calculated from the measured strain using τ=ε/A_(plate)

where A_(plate) is the area of the cantilever 20 moving in the fluid of interest, assuming a pure shear motion. The estimation of viscosity above is for a Newtonian fluid (temperature and pressure effects are neglected). For non-Newtonian (viscoelastic) fluids, the stress is given by a tensor and various models such as Kelvin-Voigt are used to estimate visco elastic properties.

In one or more embodiments, the cantilever 20 can be actuated at two or more different frequencies that provide for measuring the viscosity of the fluid of interest at two different shear rates. By measuring the viscosity at two or more different shear rates, the fluid of interest can be identified and the viscoelasticity determined.

In one or more embodiments, the actuation force or stimulus force applied by the actuator 21 to the cantilever 20 is controlled to maintain the strain measured by the sensor 24 at a constant value. The constant value of strain relates to maintaining the cantilever 20 in a constant position after deflection in the fluid. A change in the current, voltage, magnetic field, or other actuation parameter or stimulus signal necessary to maintain the constant value of strain is then proportional to the damping effect of the fluid of interest and can be used to derive the viscosity and density of the fluid. A feedback control circuit 40 as illustrated in FIG. 4 can be used to control the actuation force to maintain the constant value of strain and to determine a change in the actuation parameter or signal necessary to maintain the constant value of strain. The feedback control circuit 40 receives an input signal 41 (i.e., feedback signal) from the one or more sensor(s) 24 and controls a stimulus signal 42 to the actuator 21, which can include the magnetic field source 30.

FIG. 5 presents one example of a method 50 for estimating a physical property of a fluid of interest. The method 50 calls for (step 51) conveying a carrier through a borehole penetrating the earth. Further, the method 50 calls for (step 52) moving a cantilever in the fluid with an actuator at a frequency less than a lowest resonant frequency of the cantilever, the cantilever being disposed at the carrier. Further, the method 50 calls for (step 53) sensing a strain imposed on the cantilever due to movement of the cantilever in the fluid using a sensor in order to estimate the property.

It can be appreciated that solid-state components such as the cantilever 20, the actuator 21, the sensor 24 and the electronic device 23 enable the instrument 7 to function in the high temperature and pressure environment experienced downhole.

In support of the teachings herein, various analysis components may be used, including a digital and/or an analog system. For example, the downhole electronics 8, the surface computer processing 9, the electronic device 23 or the feedback control circuit 40 may include the digital and/or analog system. The system may have components such as a processor, storage media, memory, input, output, communications link (wired, wireless, pulsed mud, optical or other), user interfaces, software programs, signal processors (digital or analog) and other such components (such as resistors, capacitors, inductors and others) to provide for operation and analyses of the apparatus and methods disclosed herein in any of several manners well-appreciated in the art. It is considered that these teachings may be, but need not be, implemented in conjunction with a set of computer executable instructions stored on a non-transitory computer readable medium, including memory (ROMs, RAMs), optical (CD-ROMs), or magnetic (disks, hard drives), or any other type that when executed causes a computer to implement the method of the present invention. These instructions may provide for equipment operation, control, data collection and analysis, data and analysis presentation and other functions deemed relevant by a system designer, owner, user or other such personnel, in addition to the functions described in this disclosure.

Further, various other components may be included and called upon for providing for aspects of the teachings herein. For example, a power supply (e.g., at least one of a generator, a remote supply and a battery), cooling component, heating component, magnet, electromagnet, sensor, electrode, transmitter, receiver, transceiver, antenna, controller, optical unit, electrical unit or electromechanical unit may be included in support of the various aspects discussed herein or in support of other functions beyond this disclosure.

The term “carrier” as used herein means any device, device component, combination of devices, media and/or member that may be used to convey, house, support or otherwise facilitate the use of another device, device component, combination of devices, media and/or member. Other exemplary non-limiting carriers include drill strings of the coiled tube type, of the jointed pipe type and any combination or portion thereof. Other carrier examples include casing pipes, wirelines, wireline sondes, slickline sondes, drop shots, bottom-hole-assemblies, drill string inserts, modules, internal housings and substrate portions thereof.

Elements of the embodiments have been introduced with either the articles “a” or “an.” The articles are intended to mean that there are one or more of the elements. The terms “including” and “having” are intended to be inclusive such that there may be additional elements other than the elements listed. The conjunction “or” when used with a list of at least two terms is intended to mean any term or combination of terms. The terms “first,” “second” and “third” are used to distinguish elements and are not used to denote a particular order. The term “couple” relates to a first component being coupled to a second component either directly or indirectly through an intermediate component. The term “disposed at” relates to a first component being disposed in or on a second component.

It will be recognized that the various components or technologies may provide certain necessary or beneficial functionality or features. Accordingly, these functions and features as may be needed in support of the appended claims and variations thereof, are recognized as being inherently included as a part of the teachings herein and a part of the invention disclosed.

While the invention has been described with reference to exemplary embodiments, it will be understood that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications will be appreciated to adapt a particular instrument, situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. An apparatus for estimating a property of a fluid downhole, the apparatus comprising: a carrier configured to be conveyed through a borehole penetrating the earth; a cantilever disposed at the carrier and configured to move in the fluid upon receiving a stimulus force; an actuator disposed at the cantilever and configured to provide the stimulus force at a frequency less than a lowest resonant frequency of the cantilever; and a sensor disposed at the cantilever and configured to sense a strain imposed on the cantilever due to movement of the cantilever in the fluid in order to estimate the property.
 2. The apparatus according to claim 1, wherein the property comprises at least one of density, viscosity, and visco elasticity.
 3. The apparatus according to claim 1, wherein the frequency is zero Hertz.
 4. The apparatus according to claim 3, further comprising a feedback control circuit configured to receive the strain as input and to control a signal to the actuator to maintain the strain at a constant value wherein a change in magnitude of the signal necessary to maintain the strain at the constant value is used to derive viscosity or density of the fluid.
 5. The apparatus according to claim 1, wherein the cantilever and a base supporting the cantilever is formed from a substrate.
 6. The apparatus according to claim 1, wherein the cantilever defines a first hole and a second hole with a center bridge element disposed between the holes, the cantilever further defining a first side bridge element adjacent to the first hole and a second side bridge element adjacent to the second hole, the first, second, and center bridge elements extending from a base to a distal end of the cantilever.
 7. The apparatus according to claim 6, wherein the sensor is disposed at the center bridge element.
 8. The apparatus according to claim 6, wherein sensor comprises a first sensor disposed at the first side bridge element, a second sensor disposed at the second side bridge element, and a third sensor disposed at the center bridge element.
 9. The apparatus according to claim 6, wherein the actuator comprises a conductive element extending from the first side bridge element to the second side bridge element and configured to conduct current to interact with a magnetic field in order to move the cantilever.
 10. The apparatus according to claim 6, wherein the actuator comprises a layer of magnetic material extending from the first side bridge element to the second side bridge element and configured to interact with a magnetic field in order to move the cantilever.
 11. The apparatus according to claim 1, wherein the actuator comprises at least one of a piezoelectric material, a conductive material, a magnetostrictive material, and a photostrictive material.
 12. The apparatus according to claim 11, wherein the conductive material is configured to conduct current that interacts with a magnetic field to move the cantilever.
 13. The apparatus according to claim 12, wherein the actuator further comprises a source of the magnetic field configured to interact with a current or magnetic material disposed at the cantilever in order to move the cantilever.
 14. The apparatus according to claim 1, further comprising an electronic device coupled to the actuator and configured to actuate the actuator at the frequency less than the lowest resonant frequency of the cantilever.
 15. The apparatus according to claim 14, wherein the electronic device is configured to provide at least one of a voltage, a current, and light to actuate the actuator.
 16. The apparatus according to claim 1, wherein the sensor comprises a strain gauge.
 17. The apparatus according to claim 16, where in the strain gauge uses a change in resistance or a magnetostrictive effect to measure the strain.
 18. The apparatus according to claim 1, wherein the carrier comprises at least one of a wireline, a slickline, a drillstring, and coiled tubing.
 19. A method for estimating a property of a fluid downhole, the method comprising: conveying a carrier through a borehole penetrating the earth; moving a cantilever in the fluid with an actuator at a frequency less than a lowest resonant frequency of the cantilever, the cantilever being disposed at the carrier; and sensing a strain imposed on the cantilever due to movement of the cantilever in the fluid using a sensor in order to estimate the property.
 20. The method according to claim 19, wherein the property comprises at least one of density, viscosity, and viscoelasticity.
 21. The method according to claim 19, wherein sensing comprises measuring the strain as a function of time with respect to a stimulus applied to the cantilever by the actuator.
 22. The method according to claim 19, wherein the frequency comprises a first frequency and a second frequency and the strain comprises a first strain corresponding to movement of the cantilever at the first frequency and a second strain corresponding to movement of the cantilever at the second frequency, the first strain and the second strain being used to identify the fluid and to estimate viscoelasticity of the fluid.
 23. A non-transitory computer-readable medium comprising computer-executable instructions for estimating a property of a fluid downhole by implementing a method comprising: moving a cantilever in the fluid with an actuator at a frequency less than a lowest resonant frequency of the cantilever, the cantilever being disposed at the carrier configured to be conveyed through a borehole penetrating the earth; and sensing a strain imposed on the cantilever due to movement of the cantilever in the fluid using a sensor in order to estimate the property. 